Electric motors are used in many application areas, such as utilities, manufacturing, military, medicine, transport, and so forth. One type of electric motor in general use is known as a brushless direct current (BLDC) motor. In a BLDC motor, the stationary outside portion (stator) is typically composed of electromagnetic windings corresponding to the electrical phase configuration of the motor, and the rotating inner portion (rotor) is typically composed of two or more permanent magnets of opposite magnetic polarity. The stator windings are generally electrically connected to a controller/driver unit, where the controller typically provides commands to the driver to generate poly-phase input currents in the stator windings. A BLDC motor driver does not require brushes or a commutator, and is therefore relatively maintenance-free, with a typically lower level of generated electrical noise.
One conventional type of BLDC motor driver includes a series of Insulated Gate Bipolar Transistors (IGBT's) electrically connected to the phase windings of the BLDC motor. For a three-phase BLDC motor, a conventional driver typically includes six IGBT's arranged in three half-bridges, where each half-bridge can generate a drive for one phase of the motor. As the rotor permanent magnets approach the stator electromagnetic windings of opposed polarity, sensors are typically used to signal the angular position of the rotor to the controller, which can then command the driver to cause the input currents in the stator windings to switch their magnetic field polarities. In this manner, a rotating magnetic field can be generated by the current flows through the stator windings. For a three-phase motor, the three current phases are typically switched in sequence, as dictated by the angular position of the rotor.
The speed of a BLDC motor is generally controlled by a pulse width modulation (PWM) technique, where the driver controls the average currents in the stator windings by generating “on” and “off” states for the input voltage signals to the stator windings. That is, the duty cycle of the input voltage pulse signals can be used as a controlling factor for the average current in the stator windings.
The upper speed capability of a conventional BLDC motor driver is typically limited to the switching speed of the IGBT elements in the half-bridge circuits used to drive the stator windings. For example, a standard driver with six IGBT's can typically drive a three-phase motor, using two IGBT's per phase, with a maximum switching frequency of approximately 20 kHz, assuming. The maximum IGBT current is not required for more than a few minutes. As such, conventional BLDC motor drivers using IGBT switching elements are generally limited to relatively low frequency (about 20 kHz maximum) and low power (about one horsepower maximum) applications.
While other switching devices with higher frequency capabilities are available, their cost is typically many times' higher than the cost of a standard IGBT, which makes the costly high frequency devices generally undesirable for production applications. Furthermore, as motor technology advances, there is an increasing demand for drivers that are capable of operating at higher frequencies and higher power levels. For example, there are current applications requiring an operating frequency in the range of 62.5 kHz, with power levels ranging from approximately 2 to 21 horsepower. Therefore, there is a need for a scalable type of driver to operate over a range of frequencies and power levels. Moreover, this type of scalable driver could be suitable for production applications if the switching elements were standard low-cost components, such as IGBT's.
Accordingly, it is desirable to provide a controller/driver for BLDC motor applications with scalable frequency and power capabilities. In addition, it is desirable to implement the scalable driver with low-cost components for production applications. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.